1. Field of the Invention
The present invention relates to a method and apparatus for testing disk drive read/write heads. In a particularly preferred embodiment, the present invention relates to a method in which a read/write head is tested before being mounted to a suspension, such that if the read/write head is found to be defective only the read/write head is wasted and not also a suspension and possibly a flexible circuit interconnect as well. In another particularly preferred embodiment, the present invention relates to a method of testing disk drive read/write heads in which a read/write head and a recordable medium such as a media paddle are caused to move back and forth with respect to each other in oscillatory fashion.
2. Description of Related Art
Hard disk drives are used in conjunction with computer systems for mass storage of information. Hard disk drives typically comprise one or more recordable media disks with a separate read/write head disposed on each side of each disk. For example, a particular arrangement may comprise a stack of ten disks and twenty read/write heads that are disposed on alternating sides of the ten disks. The placement of read/write heads on both sides of a disk permits information to be written to and read from both sides of the disk.
A typical read/write head comprises a read head and a write head both of which are disposed on a single substrate. Substrates typically are vitrified (glass) or oxidized metals (ceramics). There are a number of types of read heads such as AMR, GMR, inductive or optical read heads, as well as others. An MR head stripe has a change in a resistance that is a function of sensed magnetic field intensity. The write head is an inductive element that produces a magnetic field for recording information on a disk.
Conventionally, read/write heads are manufactured using a process that results in multiple read/write heads being disposed in a row on a single substrate wafer. Most such wafers today are A1203TiC2(xe2x80x9cA1TiCxe2x80x9d). The wafer is then sliced and a row is adhesively mounted on a xe2x80x9crow barxe2x80x9d or xe2x80x9ctransfer toolxe2x80x9d where the row is electronically lapped and then cut to produce discrete read/write heads (the opposite order is also possible as well as other processes). The individual read/write heads are then removed from the row bar, mounted to the suspension and then tested.
To test a read/write head, an arrangement is used that is quite similar in operation to a fully assembled disk drive. In particular, a spinning disk tester or xe2x80x9cspinstandxe2x80x9d tester is used in which the read/write head writes information to and reads information from the spinning disk as the spinning disk rotates. To enable the read/write head to be tested in this manner, the read/write head is first mounted to a suspension that maintains the read/write head in close proximity to the spinning disk. The suspension accommodates height variations of the read/write surface of the spinning disk, which is used as a recordable medium for writing and reading information, so as to maintain the proper gap between that surface and the read/write head. Typically, the read/write head is electrically connected to electronic test equipment by way of a flexible circuit interconnect that connects to connection pads on the read/write head.
If the read/write head passes the tests that are applied, then the read/write head, the suspension, and the flexible circuit interconnect are incorporated into a hard disk drive. The mounting of the read/write head to the suspension is therefore permanent to the extent that the read/write head remains mounted to the suspension when the read/write head is finally assembled into a disk drive. The same is also true with respect to the flexible circuit interconnect.
On the other hand, if the read/write head is found to be defective, then both the read/write head and the suspension are discarded. Thus, once the read/write head is mounted to the suspension, both the read/write head and the suspension are either used or not used. It is not cost-effective to attempt to remove the read/write head from the suspension and remount another read/write head to the suspension in the event that the read/write head is found to be defective. Again, the same is true with respect to the flexible circuit interconnect.
Economically, this approach is highly disadvantageous. It costs roughly the same amount to manufacture the suspension and mount the read/write head to the suspension as it costs to manufacture the read/write head itself. Further, a typical yield rate for read/write heads can vary between 5% to 90%. In other words, if the yield is 25%, for example, for every four read/write heads that are manufactured, an average of three will be found to be defective. Because both the read/write head and the suspension are discarded when the read/write head is defective, three out of four suspensions that are manufactured will be discarded, even though it is the read/write heads that are defective and not the suspensions. The fact that non-defective suspensions must be discarded, according to current read/write head testing methods costs the magnetic recording head industry millions of dollars per day or more in unnecessary waste. An alternative method and system in which read/write heads could be tested without mounting the read/write heads to a suspension, thereby reducing or eliminating unnecessary waste when a given read/write head is defective, would be extremely beneficial.
To overcome these drawbacks of the prior art, the present invention provides improved methods and systems for testing disk drive read/write heads.
According to a first aspect of the invention, a method is provided that comprises manufacturing a read/write head for a disk drive; then testing the read/write head; and then mounting the read/write head to a suspension only after the testing step indicates that the read/write head is not defective. Preferably, the testing step further includes writing information to a recordable medium; and then reading the information from the recordable medium. During the performance of the writing and reading steps, the read/write head and the recordable medium are caused to move back and forth with respect to each other in oscillatory fashion without the recordable medium spinning. Preferably, the recordable medium is a non-disc shaped media paddle.
According to a second aspect of the invention, a method of testing a read/write head for a disk drive comprises causing the read/write head and a recordable medium to move back and forth with respect to each other in oscillatory fashion; and testing the read/write head while the read/write head and the recordable media are being caused to move with respect to each other. Preferably, the recordable medium oscillates and the read/write head is generally fixed. In an especially preferred embodiment, the recordable medium is a media paddle having first and second ends. The first end of the media paddle is fixedly mounted to a support structure. The second end moves immediately adjacent the read/write head, in particular, back and forth between first and second positions as the oscillator oscillates. The testing step then includes writing information to the second end of the media paddle using the read/write head and then reading the information from the second end of the media paddle using the read/write head.
According to a third aspect of the invention, an apparatus for testing a read/write head of a disk drive comprises an oscillator, a non-disc shaped recordable medium, and a processor. The oscillator preferably has a surface that oscillates in at least one dimension while testing and another dimension while landing. The oscillator is driven with a periodic signal but not necessarily a sinusoidal signal. Most preferably, the signal has regions in which the signal increases and decreases linearly between maxima and minima, to promote linear (constant speed) movement of the media paddle. To the extent that the driven paddle motion is nonlinear, the bit spacing will vary on the media but the readback frequency will not change (due to the fact that a similar variation in bit spacing occurred during writing) and thus all standard magnetic recording testing can be applied. The recordable medium is mechanically coupled to the oscillator, and is moveable in accordance with the movement of the surface of the oscillator. Thus, the recordable medium moves back and forth with respect to the read/write head in oscillatory fashion when the oscillator is driven with the periodic signal. Preferably, another identical oscillator which is driven out-of-phase mounted in a collocated manner is utilized to cancel unwanted noise and vibration. The test or channel processor is capable of being electrically coupled to the read/write head to be tested and of using the read/write head to write information to and read information from the recordable medium to test the read/write head.
In an alternative embodiment, an effector mechanism may be used to grasp the read write head relative to a spinning media. The effector mechanism may be controlled using an arrangement similar to the positioning assembly used for the media paddle, as discussed above. Like the above embodiment, this arrangement permits the read/write head to be tested before mounting of the head to a suspension.
Other objects, features, and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many modifications and changes within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.